This invention relates to a method and apparatus for the cultivation of plants and, more particularly, plants such as edible mushrooms which require a closely controlled environment in which to propagate.
Mushrooms are very sensitive, requiring careful control of compost fermentation; sanitization of the beds, trays and utensils for fungus and pest control; exact temperatures for pasteurization and incubation of the spawn; and control of the temperature during the growing and harvesting period. Equally important are the regulation of humidity, filtration and circulation of the air, the supply of water, and the removal of carbon dioxide and other gases which are produced during the growing period.
Currently, there are two principal systems of commercial mushroom cultivation: the "shelf" system and the "tray" system. In the shelf system, the mushrooms are grown in a growth medium or compost placed in stationary beds on tiers of shelves in mushroom houses, abandoned mines or unused railway tunnels. Systems of this character require considerable physical and mechanical labor. In order partially to mechanize mushroom cultivation, many growers use the tray system (also referred to as the "two zone" system) requiring two and/or three separate rooms: one for pasteurizing the compost, one for growing the mushroom spores (spawn) in the filled trays, and another for growing the mushrooms. Unlike the immovable beds of compost in the shelf system, the tray system utilizes trays or frames of compost which can be moved from one area to another. This method of production can be used when a large, natural growing area is available, such as a mine or tunnel. Such areas are suitable for year-round growing but too expensive to heat for the necessary pasteurizing process; accordingly, separate small buildings must be constructed for pasteurizing and spawning. Mechanical means are used for moving the trays between the separate areas for each of the phases.
Although each grower has his own method, facilities, temperatures and time schedule, the following procedures are generally followed:
After composting, the beds or trays are filled either in the growing house itself for the shelf system or, if using the tray system, in a separate area. The beds or trays are then pasteurized to control harmful fungi, insects and nematodes. All ventilation is stopped; the temperature of the beds is allowed to rise to the required level and is maintained the required period of time to effect pasteurization. The room is then ventilated, and the temperature is dropped to the appropriate level for planting (spawning).
Once pasteurized, the beds or trays are "planted" with spawn either by hand or with a spawning machine. During the spawn run, correct humidity, ventilation and temperature must be maintained and the compost kept moist. Periodically, each bed or tray is checked for diseases or pests and watered. In some establishments, separate rooms are used for pasteurization and spawning. If trays are not removed to a separate spawning room, they frequently are restacked from the close pasteurization position to allow more room for necessary ventilation. This requires additional labor.
When cultivating the Agaricus variety mushroom, a 1" layer of top soil, peat, or other suitable material (casing soil), is spread on each bed at an appropriate time. The casing must be previously sterilized to kill any diseases by heating to 140.degree. F.+ and the soil must be neutralized if acid. After casing, the trays are transported to the growing room. This step is not necessary for other varieties of mushrooms which do not require a casing soil.
Watering is required periodically until small mushrooms (pinheads) appear. After the mushrooms appear, the temperature is lowered to an appropriate temperature for the mushroom variety being cultivated. This improves growth and discourages diseases and insects. Proper humidity must be maintained at all times.
Once the growing period is completed, the spent compost is usually pasteurized for four hours to destroy pests and then removed. The growing room is then cleaned of all debris and readied for the next crop.
The prior art systems do not make efficient use of the volume of the enclosed growing room. Because optimum mushroom growth is obtained only within a narrow range of air temperatures, the vertical separation between the lowest and highest beds has been limited. Despite the use of fans to circulate air within the growing rooms, it has been difficult to move air currents across the beds in a uniform manner in a room crowded with beds which are relatively close together, creating large pockets of static air, and to maintain the air temperature differential within a narrow range for more than a small portion of the vertical height of the room. It has been found that limiting air temperature differentials exceeding about 2.degree. C. adversely affect growth. In growing rooms, which are often twelve to fourteen feet high, there will often be a temperature differential of 6.degree. C. between the floor and ceiling. This is one reason stationary bed growers only grow on trays or beds five or six tiers high. Even in this narrow range, the trays in the center will receive the optimum temperature and thus normally provide the greatest yield with the lowest and highest beds suffering the most. If a larger number of tiers were employed, the resulting larger temperature differential and lack of adequate air circulation would be inimical to effective growth in the additional trays.
The prior art systems are labor intensive. Watering is usually done by hand, and thus it is almost impossible to water each tray equally or evenly. Some types of mushrooms, such as the Volvariella variety, require exposure to a controlled amount of light; but this becomes more difficult as the number of trays in a given area is increased.